Defined Benefit Postretirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Amortization:
Net settlement loss	$ 6	$ (2)	$ (1)	$ (9)
Estimated future contributions over the remainder of the current year	7		7
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	5	14	14
Interest cost	2	3	7	17
Expected return on plan assets	(2)	(3)	(7)	(19)
Amortization:
– prior service credit	(1)	(1)	(5)	(5)
– actuarial loss	2	2	7	6
Net settlement loss	9	0	25	2
Net curtailment gain			(3)	0
Net periodic benefit costs (credits)	14	6	38	15
Pension Benefits | U.K.
Amortization:
Reclassifications from AOCI upon remeasurement		20		20
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	1	1	2	3
Expected return on plan assets	0	0	0	0
Amortization:
– prior service credit	(4)	(5)	(13)	(14)
– actuarial loss	0	1	1	1
Net settlement loss	0	0	0	0
Net curtailment gain			(14)	0
Net periodic benefit costs (credits)	$ (3)	$ (3)	(24)	$ (10)
Payment for other postretirement benefits			11
Funded Plan
Amortization:
Payment for pension benefits			21
Unfunded Plan
Amortization:
Payment for pension benefits			$ 17